Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Direct Offering [Member]	At-The-Market Offering [Member]	Common Stock [Member]	Common Stock [Member] Direct Offering [Member]	Common Stock [Member] At-The-Market Offering [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Direct Offering [Member]	Additional Paid-in Capital [Member] At-The-Market Offering [Member]	Accumulated Deficit [Member]
Beginning Balances at Dec. 31, 2019	$ 69,049			$ 2			$ 539,158			$ (470,111)
Beginning Balances, shares at Dec. 31, 2019				15,001,795
Issuance of common stock upon exercise of options	33						33
Issuance of common stock upon exercise of options, shares				5,645
Issuance of common stock under employee benefit plans, shares				8,492
Stock-based compensation	717						717
Net loss	(10,796)									(10,796)
Ending Balances at Mar. 31, 2020	59,003			$ 2			539,908			(480,907)
Ending Balances, shares at Mar. 31, 2020				15,015,932
Beginning Balances at Dec. 31, 2020	48,055			$ 2			548,707			(500,654)
Beginning Balances, shares at Dec. 31, 2020				16,481,099
Issuance of common stock upon exercise of options	$ 260						260
Issuance of common stock upon exercise of options, shares	77,858			77,858
Issuance of common stock, net of issuance costs		$ 20,866	$ 7,034					$ 20,866	$ 7,034
Issuance of common stock, net of issuance costs, shares					2,875,000	884,695
Stock-based compensation	$ 505						505
Net loss	(8,004)									(8,004)
Ending Balances at Mar. 31, 2021	$ 68,716			$ 2			$ 577,372			$ (508,658)
Ending Balances, shares at Mar. 31, 2021				20,318,652